1. Field of the Invention
This disclosure relates to a hearing aid device.
2. Description of the Related Art
Hearing aid devices developed for people with hearing impairment use a gain controller to amplify sound picked up by a microphone, and output louder sound from a speaker. This has made it much easier for patients to recognize sounds. However, when a gain controller is used to amplify sound picked up by a microphone, and a louder sound is merely emitted from a speaker in this way, the hearing aid effect may not be adequate, particularly in terms of understanding a conversation. One reason for this is that speech is made up of vowels (bass) and consonants (treble). Specifically, a hearing-impaired person often finds it particularly difficult to hear sounds in the high-frequency band, that is, consonants. Such inability to pick up consonants impedes the person's ability to follow a conversation.
One way to deal with this problem is to further raise the amplification of the gain controller. However, when the amplification is thus raised, the sound pressure (volume, sound level) also rises for vowels, which creates a situation in which the consonants are drowned out in the vowels (called masking), and as a result, the hearing aid effect is inadequate for following a conversation, as discussed above. In view of this, in the following Non-Patent Literature 1 there is proposed a dichotic hearing aid in which a first hearing aid worn on one ear is used for low pitch sounds, and a second hearing aid worn on the other ear is used for high pitch sounds. That is, the user hears the vowels (low pitch sounds) in a conversation with the first hearing aid, and hears the consonants in a conversation (high pitch sounds) with the second hearing aid. The user's brain merges these into a single sound, and this makes conversation easier to understand.    Non-Patent Literature 1: Y. Suzuki et al., “Determination of Filtering Parameters for Dichotic-Listening Binaural Hearing Aids,” Acoustic 08 Paris (France), 2008
As discussed above, with what is discussed in Non-Patent Literature 1, a first hearing aid that is worn on one ear is used for low pitch sounds (vowels), and a second hearing aid that is worn on the other ear is used for high pitch sounds (consonants). As a result, there is no masking due to low pitch sounds (vowels) with the second hearing aid used for high pitch sounds (consonants), which means that conversation can be heard more clearly.
Nevertheless, depending on the voice characteristics, the above-mentioned dichotic hearing aid may not always afford a sufficient clarity improvement effect.